tailieunhanh - An Introduction to Thermodynamics phần 3

nó có thể ngạc nhiên khi tìm thấy như thế nào đến nay người ta có thể đi theo hướng điều trị hóa chất và cân bằng vật lý mà không cần sử dụng bất kỳ mô hình đơn giản hóa hoặc đào sâu vào lý thuyết về cấu trúc phân tử. Tách rời của nhiệt động lực học từ lý thuyết phân tử là một tài sản quan trọng. | It should also be possible to relate the volume of any liquid or solid to its temperature and pressure or to express such other properties as refractive index heat capacity at constant volume or pressure thermal conductivity heats of vaporization or fusion or vapor pressures of solids or liquids in terms of the temperature and pressure. Some of these equations will be encountered in later chapters. Thermochemistry The application to chemical reactions of the principles developed thus far is called thermochemistry. In particular the heats of reaction are measured and tabulated and from these and from measured heat capacities the enthalpy changes are calculated for other reactions or for other experimental conditions. HESS S LAW. The enthalpy change for a chemical reaction such as the oxidation of sulfur dioxide to sulfur trioxide 2 SO2 g O2 6 2 SO3 liq can be expressed as the difference between the enthalpies of the initial and final states. . ll H H MH reaction H final H initial H 2 SO3 - H 2 SO2 - H O2 There is no way within thermodynamics of measuring an absolute energy 16 or an absolute enthalpy. Only energy and enthalpy changes can be determined. However knowing that these energy and enthalpy changes depend only on the initial and final states it is possible to add and subtract chemical reactions and add and subtract the corresponding enthalpy changes. That is we may quite arbitrarily select a reference energy and or enthalpy level and measure all values from that arbitrary level. In particular it is possible to tabulate heats of formation the enthalpy changes in the reaction of the elements to form each compound and from these to calculate enthalpies of other reactions. This principle is known as Hess s law. The reactions for the formation of the gases SO2 and SO3 from the elements are S O2 - SO2 S 3 2 O2 - SO3 liq without changing their effect and therefore decreases the pressure on the walls requiring the supplement to P to fit the ideal gas equation form .